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Alikhan & Hocker dermatology > 1.2 EMBRYOLOGY > Flashcards

1.2 EMBRYOLOGY Flashcards

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Dermatology Board Prep flashcards
1
Q

Skin structures derived from two of three primary germ layers. Which ones?

A
  • Ectoderm
  • Mesoderm
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2
Q

Ectoderm gives rise to ?

A
  • epidermis
  • adnexal structures
  • Merkel cells
  • melanocytes (neural crest)
  • nerves (neuroectoderm)
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3
Q

Mesoderm gives rise to?

A
  • fibroblasts
  • LCs
  • vessels
  • inflammatory cells
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4
Q

When does formation of the epidermis start?

A

5 weeks

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5
Q

Epidermis 5th week of fetal life

A

Formation of outer periderm and inner basal epidermal layer

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6
Q

Epidermis 8th week of fetal life

A

epidermal stratification

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7
Q

Epidermis 9-12 weeks of fetal life

A

melanocytes, LCs, and Merkel cells migrate into the epidermis

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8
Q

Epidermis at Late second trimester

A

terminal differentiation, with full stratification

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9
Q

Formation of basement membrane, dermis, and subcutis begins at … weeks with the appearance of …

A

6-8 weeks

fibroblasts beneath the epidermis

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10
Q

When is the DEJ present?

A

9 weeks

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11
Q

primordial vasculature is formed at?

A

9-12 weeks

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12
Q

initial fat formation in subcutis begins at ?

A

16–18 weeks

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13
Q

Fetal skin dermis at 20 weeks?

A

mature thickness of dermis and dermal ridges present

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14
Q

EM of the Developing Human Epidermis at 6-8 weeks

A
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15
Q

EM of the Developing Human Epidermis at 7-9 weeks

A
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16
Q

EM of the Developing Human Epidermis at 22 weeks

A
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17
Q

dermis and hypodermis arise from the … component of the developing somite.

A

Dermatome

18
Q

Cartoon showing the dermatome component of the somite

A
19
Q

immunohistological features of fetal skin dermis layer

A
  • Collagen type I is the principal component of ECM (also in adult skin)
  • Collagen type III high ratio to collagen type I (than adult skin)
  • Glycosaminoglycans (GAGs) level higher (than adult skin)
  • Hyaluronic acid and chondroitin sulfate both higher
  • Elastin was not present (found in adult skin)
20
Q

What is the vernix caseosa?

A

white, creamy, naturally occurring biofilm covering the skin of the fetus during the last trimester of pregnancy

21
Q

What is the utility of vernix caseosa?

A
  • protects the newborn skin
  • facilitates extra-uterine adaptation of skin in the first postnatal week if not washed away after birth
22
Q

Vernix caseosa features

A
  • a highly variable coating of the fetal skin

high water content (80%) largely compartmentalized within fetal corneocytes (cells forming the stratum corneum)

  • develops cranio-caudally production coincides in utero with terminal differentiation of the epidermis and formation of the stratum corneum
  • primarily composed of sebum, cells that have sloughed off the fetus’s skin and shed lanugo hair
  • can be absent in preterm infants
  • dehydration and rehydration processes occur two to four times faster at 37 degrees celcius than at room temperature[10]
  • towards term fragments of vernix can mix into the amniotic fluid resulting in (normal) turbidity
  • fetal swallowing of amniotic fluid mixed with fragments of vernix can also occur
  • cathelicidin LL-37, alpha-defensins, and LL-37 in neutrophils
23
Q

initial follicle development on the eyebrows, scalp, upper lip, and chin begins at … weeks

– spreads …

epidermal placodes (derived from ectoderm) induce underlying dermal papilla formation (derived from mesoderm)

A

9-12 weeks

caudally & ventrally

24
Q

hair canal is fully formed at?

A

18–20 weeks

25
Q

initiation of cycling through anagen, catagen, and telogen begins at ?

A

24-28 weeks

26
Q

… is an important molecule for telogen to anagen transition

A

Sonic hedgehog

27
Q

Nails formation timeline

A

■ 8–10 weeks: nail bed demarcation

■ 12 weeks: proximal nail folds formed

■ 17 weeks: nail plate formed, covers nail bed by week 20

28
Q

eccrine gland anlage formation on palms and soles starts at?

A

10 weeks

29
Q

eccrine primordia bud down, glands begin to develop

A

14–16 weeks

30
Q

initiation of truncal eccrine gland formation

eccrine glands and ducts nearly mature on volar skin

A

22 weeks

31
Q

Apocrine gland formation initiated later than eccrine glands, at ..?

A

22 weeks

32
Q

Sebaceous gland formation parallels … (derived from …)

A

hair follicle development

outer root sheath

33
Q

Melanocytes are neural crest-derived cells, migrate under the direction of … & …

A

KIT and KIT ligand

34
Q

melanocytes are present in epidermis at?

A

12 weeks

35
Q

melanin production begins at?

A

12-16 weeks

36
Q

melanocytes proliferate and become fully functional (transfer melanosomes to keratinocytes) at?

A

16-20 weeks

37
Q

Epidermal stem cells are responsible for ?

A
  • maintenance
  • repair
  • renewal of epidermis
38
Q

Keratinocyte stem cells located within the … of the hair follicle and at the … of interfollicular epidermis

A

bulge region

base of rete ridges

39
Q

Complete renewal of epidermis occurs every?

A

40 to 56 weeks

40
Q

Asymmetric division gives rise to …, which divide rapidly to produce …

A

transient amplifying cells

terminally differentiated cells

41
Q

Stem cells are … with unlimited capacity to divide

A

multipotent

Alikhan & Hocker dermatology (16 decks)

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